Consider a full binary tree with $n$ internal nodes, internal path length $I$, and external path length $e$. the internal length of a full binary tree is the sum, taken over all nodes of the tree, of the depth of each node. Similarly, the external path length is the sum, taken over all leaves of the tree, of the depth of each leaf.
Which of the following is correct for the full binary tree?
- $e=i+n$
- $e=i+2n$
- $e=2i+n$
- $e=2n+i$